Alkaline cells are well known in the art and generally employ a zinc anode, manganese dioxide as the cathode with an aqueous solution of potassium hydroxide for the electrolyte. These cells are readily available commercially for industrial and home applications. Recently a new type of alkaline cell was disclosed by Cegasa International, a Spanish company. This cell, referred to as an air-assisted cell, employs zinc as the anode and manganese dioxide as the cathode with an aqueous solution of potassium hydroxide as the electrolyte. This cell is designed so that the positive electrode containing the manganese dioxide (MnO.sub.2) is supported about its periphery and along its full length in the cell by a perforated ribbed air distribution grid. The bottom or negative end of the cell has an insulating support which allows air to enter the cell and pass up along the outside of the supported positive electrode. When the cell is initially put into a circuit, the electrochemical reaction depends primarily upon the presence of the manganese dioxide cathode. As the reaction progresses, and the manganese dioxide cathode is electrochemically reduced, air within the cell reoxidizes and recharges the manganese dioxide. Thus an air-assisted cell is designed to use oxygen in the air to "recharge" manganese dioxide in the cathode. This "recharging" of the manganese dioxide means that the fixed quantity of manganese dioxide in the cathode can be discharged and then recharged numerous times.
Standard alkaline batteries and air-assisted alkaline batteries have traditionally been made with mercury in the anode. Mercury helped to prevent gassing by raising the hydrogen overvoltage. Due to concerns about the environment, battery manufacturers are designing alkaline batteries with little or no mercury. As the percentage of mercury in the cells has been reduced, problems with leakage and decreased shelf life have become apparent. The reduction or elimination of mercury has led to service and shelf storage problems because gassing in and the expansion of the anode in the anode compartment have forced electrolyte to flow from the anode compartment into the cathode compartment. As electrolyte moves from the anode into the cathode, ionic conductivity in the anode decreases and the cell cannot discharge efficiently. If the anode compartment continues to gas and expand, the electrolyte from the anode could be driven into the cathode and may essentially be driven through the seal and out of the cell. In addition, the reaction products of certain alkaline cells take up a greater volume than the initial components and thus could further create pressure buildup within the cell. To compensate for anode expansion, a void cavity has been provided above the anode compartment to accommodate anode expansion and gassing. This solution, although somewhat effective, reduces the amount of active anode material assembled in the cell and thus reduces the cell output capacity.
U.S. Pat. No. 4,726,779 disclosed a galvanic primary cell in which the anode mixture of a zinc-alkaline electrolyte gel is displaced by the introduction of a hollow body into the concentrically arranged anode space so that the zinc powder is fixed in a layer oriented toward the cathode of the cell, ensuring proper discharge, and so that the aqueous portion of the anode mixture can escape inside the displacement body through narrow openings in the body's wall. By attaching the displacement body to the negative electrode conductor, the current drainage can be improved by making at least part of the displacement body of a metallically conducting material.
U.S. Pat. No. 3,069,485 disclosed a cell comprising a cupped metallic container, an inner and an outer metal bottom, a separator-lined cathode fitting in said container, a top closure, a tubular semi-rigid swellable anode fitting in said cathode but separated therefrom by said separator and an inert tubular metallic conductor fitting in contact with said anode, said conductor being composed of a material which is unaffected by the electrochemical reactions in said cell, and being secured to said inner metal bottom by means of a rivet also contacting said outer metal bottom and an insulating grommet surrounding said rivet and insulating said rivet and said collector from said inner bottom.
U.S. Pat. No. 3,156,585 discloses a hermetically sealed battery in which the innermost electrode is also a hollow cylinder composed of a plurality of part-cylindrical elements, with a perforated resilient sleeve fitting in the central bore, and there is provided a space in the center of the battery which functions as a diffusion space. The resilient sleeve can readily be inserted into the central bore by merely contracting the sleeve radially, and the sleeve tends to expand within the bore by its own resiliency to establish positive pressure contact of the same with the innermost or central electrode of the cell as well as between the electrodes and separators. The connection of the central electrode to the corresponding terminal is also effected in a simple and positive manner by the mere pressure fit of the resilient sleeve into a central recess formed in a cover plate.
U.S. Pat. No. 4,054,726 discloses a zinc-air alkaline primary cell which includes a metal cover containing a negative zinc electrode and a metal cup containing a positive air electrode. The cover is sealed to the cup which has an air inlet by means of a gasket. Zinc active material of the zinc electrode may be in the form of a compressible body or may comprise zinc powder in which a compressible body is embedded, so as to provide space to compensate for expansion of the zinc active material during use of the cell.
U.S. Pat. No. 3,920,475 discloses an alkaline galvanic cell in which free access of air oxygen to the positive electrode along the height and cross-section of the electrode as well as for hydrogen escape from the negative electrode is provided by having axial extending passages made in the body of the positive electrode, said passages preferably being of arcuate shape in a cross-section and the body of the negative electrode also provided with axially extending passages.
It is an object of the present invention to provide a galvanic cell with a gas filled collapsible member within the anode compartment to accommodate expansion of the anode during shelf storage and/or discharge.
It is another object of the present invention to provide a galvanic cell with improved capacity while maintaining good service and shelf performance.
It is another object of the present invention to provide means to retain the anode's electrolyte within the confines of a separator encasing the anode.
It is another object of the present invention to provide an efficient and cost effective alkaline cell.
The above and further objects will become apparent upon consideration of the following description and drawings thereof.